1. Field of the Invention
The present invention relates to an image processing apparatus, image capturing apparatus, control method, and recording medium, and particularly to a technique for generating an image focused at an arbitrary focal length from an image signal after imaging.
2. Description of the Related Art
In recent years, a technique for recording a distribution of strength and traveling direction of light at the time of imaging as output data, and generating an image focused at an arbitrary focal length from the output data after recording in an image capturing apparatus such as a digital camera has been proposed.
Ren Ng, et al., “Light Field Photography with a Hand-Held Plenoptic Camera”, Stanford University Computer Science Tech Report CTSR 2005-02 discloses a method (Light Field Photography) of separately recording light fluxes entering from various directions by focusing light fluxes which have passed through different pupil regions of an imaging lens on respective pixels (photoelectric converters) of an imaging element via a microlens array. In Light Field data (LF data) obtained in this way, neighboring pixels record light fluxes entering from different directions, and light fluxes in the same direction are extracted from pixels associated with respective microlenses, thereby generating an image captured from that direction. An arbitrary focal length is set, and outputs from pixels which record light fluxes that have passed through one point on a focal plane of that focal length are added, thereby generating (reconstructing) pixels of an image focused at the specific focal length after imaging in a pseudo manner.
The LF data recorded using the Ren Ng's method cannot be browsed in a state that allows the user to recognize the contents of an object before a focal length is set, and a reconstructed image focused at the focal length is generated, as described above. For example, by generating a thumbnail image to be focused at one focal length for each LF data, the user may choose LF data which captured a desired scene.
However, in such thumbnail image focused at one focal length, which is generated from the LF data, since images of objects focused at focal lengths different from that focal length are blurred, the user cannot recognize the objects. That is, the user cannot specify the LF data which captured a scene including a desired object.